If your charity is lucky enough to have people running for you, you could potentially be in-line to receive more than just the money they have raised by doing the run. With a good relationship building policy in place you could earn a lifetime supporter for your charity.
Planning ahead, you could schedule a well done email or a phone call after the run. If you have a representative of the charity at the run, you can take pictures to be used in the thank you emails and on social media. If you don't have pictures yourself you can ask your runners for them in the thank you email and use them in your next charity newsletter. All this is strengthening your relation with runners by showing you're genuinely grateful for their efforts and interested in their achievement.
The day after the run you could send an email out to your runner with tips on how to sooth sore muscles and joints, again showing you care about them on an individual level. You could also send them a premade thank you poster to use on their social media to thank those that sponsored them. This has the added bonus that you can put your charity branding on there! Don't forget to thank those that sponsored your runner yourself too.
If all this sounds too complex or time consuming, it really needn't be. CRM software like Ribbon CRM makes it easy to segment your database of contacts into those who are running for you and those who aren't. It can schedule one email to be sent out to that segmented list of multiple people so you only have to type it out once. You can also set reminders against a specific supporter accounts or general reminders along with notes so you know when you last contacted a person. You'll also have all this data next year so you know who to contact to see if they'd like to run for your charity again (and show that you remembered they ran it for you the previous year!).